This has confounded me for a long long time, the first computer I owned was a Color Computer 3, getting the 80 column display in this thing was a bear unless you opted for an expesive monitor that only worked with this computer. Well, I've gotten back in to vintage computing, and have a pair of Commodore 128s, and Commodore 64C. While the 64 doesn't need anything beyond hooking up to the RCA inputs and getting the standard 40 column out of a TV and a Commodore 1702 monitor, the 128s pose something of a problem. The coversion from RGBI (Red Green Blue Intensity) and if it is done incorrectly you get dark yellow instead of brown AND in most cases only 8 of the 16 colors available on this 8bit computer.
There are a plethora of converters out there, but they are expensive, I am hoping, since you were able to make a portable Atari 2600 that only had RF in the beginning, that you might have some insight to a less expensive and spot on approach to this.
